The present invention relates to a bearing assembly for supporting a high speed element such as the rotor of an aircraft engine and, more particularly, to a rotor support bearing assembly for use in an engine operating environment wherein environmental temperatures span the range cold state to as high as 1500 degrees F.
Aircraft jet engines operating at relatively low temperatures present no especially difficult problems regarding proper rotor support and lubrication requirements. If lubricant temperatures do not exceed about 300 degrees F., the lubricants can be retained for reasonably good service life. On the other hand where engine temperatures are dramatically increased and lubricants used in the engine exposed to temperatures as high as 600 or 700 degrees F., such lubricants must receive special treatment after each use such as addition of thinners. Rotor support bearing assemblies used under conditions as aforesaid do not particularly present a drawback. On the other hand, there is constant demand for increased engine capacities and this demand carries with it higher engine operation temperatures, temperatures such as in the range 1200 to 1500 degrees F. Aside from the expense of providing lubricants satisfactory for use at such temperatures even if they could be used with conventional metallic bearing units and bearing supporting structure, there is the problem that metallic bearing units are not envisioned as satisfactorily performing at the higher engine temperatures. High temperature, dry or non-lubricated, ceramic matrix composite bearings can be used but conventional metallic bearing attachment modes, if used with a ceramic bearing unit will result in extremely high inner race thermal stresses and outer race looseness. This is because conventional metallic bearing attachment methods do not negate differential thermal growths as will occur where a ceramic bearing unit is embodied in the engine by means of metallic support structure. Also conventional attachment techniques do not allow that the bearing unit will be kept rigidly clamped throughout engine operation.